Known prior art to this invention is disclosed in U.S. patents to Frohback et al. No. 3,371,154; Frohback No. 3,391,247; Hodge No. 3,446,914; Neeussen et al. No. 3,829,610; Wohlmut No. 3,848,095; Mes No. 3,931,457; and Romeas No. 4,106,058, for example, such disclosures being incorporated herein by reference.
The video track transfer system as disclosed and claimed herein is suitable for use with the system and method for reproducing pictures and related audio information as disclosed in co-pending and commonly assigned U.S. patent application to Jerome Ser. No. 73,939 filed Sept. 10, 1979 and entitled "SYSTEM, METHOD AND RECORD MEDIUM FOR REPRODUCING PICTURES AND RELATED AUDIO INFORMATION."
As shown in the incorporated references above identified, video disc and other record media such as magnetic tape have found increasing use and popularity for recording and reproducing television (TV) pictures with sound. Generally, the picture is scanned in discrete frames on a line-by-line basis, the audio information is concurrently recorded with video and audio analog tracks being formed on the record medium. The recorded information is transcribed from the record medium to simultaneously reproduce picture and sound. In such systems the reproduced audio and video signals are approximately coextensive in time.
There have also been approaches to utilize video discs for the reproduction of TV pictures and sound where the sound for each frame is of greater duration than the signal for the TV frame itself, for example, to display a still picture with an extended spoken description or explanation concerning the picture which is particularly useful for teaching or training purposes. A representative system is shown, for example, in U.S. Pat. No. 3,829,610 which shows a system employing a record disc having several concentric tracks of video information in one region of the disc and one or more helical sound grooves in another region with the sound information for each of the video tracks extending over several convolutions of sound grooves. Systems of this type have certain limitations and disadvantages in that separate heads for the sound and picture are relatively expensive, difficult to align and maintain in alignment.
The approach in the above identified co-pending application is to record video information for discrete frames of a TV picture on spaced apart tracks on a record medium such as a disc, recording extended audio information for each frame in a plurality of individual tracks between the video tracks, reading the information from one of the video tracks to reproduce one frame of the picture, and reading the information from successive ones of the corresponding audio tracks to reproduce the extended audio information. The audio tracks for each frame are positioned in relation to the video tracks such that the audio and video tracks are scanned simultaneously by a single reading head.
The information is recorded photographically and read optically. The audio information is recorded in a highly compressed format to further extend the amount of audio information for each frame of the TV picture.
Initially, when all the information was retrieved from a respective video track and its corresponding audio tracks, the reading head was shifted from one track set of a video track and its audio tracks to the next track set through a galvanometer mirror mechanism. The mirror was stepped by the controller sequentially through each of the several tracks until the head was properly positioned on the appropriate successive track set.
Now, an individual step of the galvanometer mirror can be carried out very quickly, less than 5 milliseconds. As a practical matter, however, stringing together a number of such steps requires that each step be carried out at a much slower rate, on the order of 250 msec. per step. Also, each such incremental step has about a 98% probability of occurring correctly so that when 10 steps were taken, the chances of ending incorrectly on a succeeding track set are significant, approximately one in five. Thus, the complete shift requires at least about 2.5 seconds, or more, to move from one video track to the next (assuming a total set of ten tracks). The time of 2.5 seconds is really too slow to be tolerable. Finally, moving the galvanometer mirror rapidly 10 times presents the problem that the stepping range of the mirror would be used up before the head can be appropriately repositioned by external carriage means.